Pesticide and fungicide comprising aqueous copper silicate

ABSTRACT

A method of producing a water soluble copper silicate by reacting a copper salt with an alkali silicate in an acidic solvent to produce an aqueous solution of acidified copper silicate capable of being used as a fungicide or pesticide.

This application has been filed under 35 USC 371 as a continuation ofPCT/AU92/00550, filed Oct. 14, 1992.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a pesticide and fungicide, and moreparticularly relates to a slow release copper silicate product that maybe used as a pesticide and fungicide, and also as an algaecide andinsecticide.

Copper compounds have previously been used as pesticides, insecticides,algaecides and fungicides in a variety of liquid and solid forms. Use ofcopper compounds as fungicides is particularly common. However, knowncopper fungicides and pesticides are generally either phytotoxic, andare therefore fatal to young plants thus restricting the manners of use,or are only able to be provided as mainly insoluble powders which losetoxicity relatively quickly, are difficult to apply in some instances(being unable to be absorbed) and are only suitable for topicalapplications where the weather conditions (wind and rain) will notadversely disperse them.

Copper silicate is known for use as a fungicide and algaecide. However,copper silicate has traditionally only been used in solid form whenprecipitated from solution. This has caused copper silicate products tobe seriously restricted in their commercial activities.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a copper silicateproduct which overcomes, or at least partly alleviates, the abovementioned difficulties.

The present invention is characterised by an aqueous solution ofacidified copper silicate for use primarily as a pesticide andfungicide. The invention is characterised by both the product and themethod of producing such a product, the method comprising reacting acopper salt with an alkali silicate in an acidic solvent to produce theaqueous solution of acidified copper silicate.

DETAILED DESCRIPTION OF THE INVENTION

In a preferred form of the invention, the mixture of the copper salt andthe alkali silicate is buffered in a pH range of about 2 to 6. This isto prevent the reaction of the components precipitating any insolublecompounds, such as silicic acid and/or copper silicate. In this respect,the solution should preferably be maintained in this pH range not onlyto maintain the solubility of the copper silicate, but also to produce ahighly active copper silicate. The pH range is preferably carefullymonitored as it is difficult to prevent the precipitation of coppersilicate while also producing a product that is not unnecessarilyexcessively acidic. Indeed, the preferred range of pH for the solutionis from 3 to 5, and this has been found to produce a highly active andhighly soluble aqueous copper silicate product.

The copper salt of the invention is preferably a water soluble coppersalt such as copper sulphate, while the alkali silicate is preferablysodium silicate. It will be noted however that, while being moreexpensive and less readily available commercially, copper acetate mayalso be utilised, while other copper salts could be copper bromide,chloride, fluoride, or nitrate. Furthermore, the alkali silicate couldbe potassium silicate. In this respect, the composition of the alkalisilicate may be described by reference to the ratio of alkali oxide tosilica, where the ratio SiO₂ :(Na or K)₂ O preferably covers a broadrange such as from 3.75:1 to 1:2.

The copper silicate of the invention thus allows an aqueous solution tobe applied to vegetation, or any type of structure or material, as aspray, thus giving improved coverage and penetration. In this respect,upon evaporation of the aqueous solvent, a largely insoluble acidicresidue of amorphous hydrous silicate of copper remains. This residueadheres to the contacted surface, and is surface active to a variety ofpests and fungi while remaining substantially non-phytotoxic. In thisrespect it will be understood that the term "non-phytotoxic" relates tothe product being non-toxic to plant life other than fungi. Furthermore,when applied to timber or other types of porous materials the coppersilicate may be absorbed into the material and upon drying remainimpregnated within the material in a substantially insoluble form. Thecopper silicate may remain active for many months regardless of theprevailing weather conditions.

The buffer system preferably comprises a weak acid and its salts, suchas acetic acid and sodium acetate or citric acid and sodium citrate. Thepreferred buffer system utilises acetic acid and sodium acetate in aratio of between 1 to 5 and 5 to 1, and in a concentration of 0.01 to10% w/w. In this preferred form, the buffer is created as a by-productof the reaction and provides a margin in maintaining the correct pH,which ideally is in the range of pH 3 to 5. However, it will beappreciated that there may not be a need for such a buffering system ifthe pH range can be otherwise carefully controlled by the use of anacid.

Thus, the present invention provides a copper silicate product for useas a pesticide or herbicide, the product being a stable, silicate rich,aqueous solution of acidified copper silicate having a pH in the rangeof 3 to 5. The present invention accordingly also provides a method ofproducing a copper silicate product for use as a fungicide or pesticide,the method comprising preparing separate batches of diluted coppersulphate, diluted sodium silicate and an acetic acid buffer, adding theacetic acid to the copper sulphate, followed by addition of the sodiumsilicate, to produce a stable, silicate rich, aqueous solution ofacidified copper silicate having a pH in the range of 3 to 5.

It will also be appreciated that the copper silicate of the inventionmay be used in a solid form if required, utilising the ability of theaqueous solution to be absorbed or adsorbed by a solid carrier medium,with the subsequent evaporation or drying of the aqueous solvent leavingthe largely insoluble acidic residue of amorphous hydrous coppersilicate either interspersed within the carrier or topically appliedthereto.

The product of the invention contains no complex organic chemicals andcan be provided in an easy to use aqueous form which may be used as afine spray for misting safely on trees or other plants and the like, oron any other type of surface such as on rocks, concrete paths, wood,bricks, or any surface as required. The product is substantiallynon-phytotoxic and has good tenacity, while also being capable of beingabsorbed into porous surfaces to provide an impregnated treated layer.This is particularly useful for use as a fungicide.

Thus, the problems that are often present in pesticides and fungicidesin solid form may be avoided by the use of the present invention in itsaqueous state. Pesticides in solid form are not only difficult todistribute such that they remain in place, but they provide only alimited ability to access awkward areas which are invariably the areaswhere pests accumulate. Furthermore, solid pesticides generally areunable to be used directly on plants, seedlings, trees, shrubs, berriesor fruit and the like, and generally must be spatially distributed overlarge areas. Further still, it is not unusual for animals such as birds,dogs or cats, or even children, to be attracted to pesticides andfungicides in solid form which often presents a serious health risk bothto animal life and human life due to the usually high toxicity of suchcompounds.

When the invention is used in its aqueous state, the residue whichremains upon evaporation of the water solvent is largely insoluble andadheres very well to the contacted surface. It may be present in anactive form for many months, and is safe for use with and around animalsor children.

While testing has not yet been completed to determine the precisemechanism which occurs within pests such as snails, it is evident thatupon contacting the residue the reaction with such pests is virtuallyimmediate, and death follows some time thereafter. Snails in particularappear to produce large quantities of mucous and upon contact of thebody of the snail with the residue of this pesticide, the snail diesapparently from dehydration which causes an overall system failure.

In order to better illustrate the present invention, an example of apreferred embodiment will now be described. However, it is to beunderstood that the generality of the invention as described above isnot to be limited by the following description of the preferredembodiment.

The method for producing the aqueous solution of acidified coppersilicate of the present invention is preferably conducted as a batchprocess. Firstly, sodium silicate having a preferred ratio of SiO₂ toNa₂ O in the range of 3.2 to 2, and having a pH range of 8 to 14 (ormore preferably 11.6 to 12.7) is diluted with water. The range ofconcentration for the sodium silicate may be from 0.05 to 20% w/w, ormore preferably is in the range 0.2 to 5.0% w/w.

At the same time, copper sulphate pentahydrate is dissolved in water andallowed to stand for between 8 and 24 hours, preferably overnight. Thecopper sulphate pentahydrate may have a concentration in the range of0.1 to 25% w/w, but is more preferably in the range of 0.5 to 10% w/w.

Finally, acetic acid is also diluted with water. The concentration ofthe acetic acid may be in the range of 0.01 to 10% w/w, but is morepreferably in the range of 0.05 to 2.0% w/w.

It will be appreciated by a person skilled in the art that theconcentrations described may be altered, provided that the approximateratios of components remain the same. Furthermore, while it is preferredto use an excess amount of acetic acid, a solution that is too acidicwill most likely be toxic or corrosive to the plant or surface to whichit is applied and thus should be avoided.

After preparation of the components referred to above, the acetic acidis added to the dissolved copper sulphate solution, with stirring. Thesubsequently obtained mixture is then added to the sodium silicatesolution, again with stirring. The total mixture is then diluted withwater. If required, dyes and or wetting agents may be added at thisstage, and the total mixture may be subjected to a final filtration, andis packaged as needed.

It will also be appreciated that the method of producing the product maybe carried out as a continuous process with some modification. In thisrespect, bulk solutions of copper sulphate, acetic acid and sodiumsilicate may be provided so as to be treated and mixed as above,provided the proportions of each are maintained, using the necessarymixing, stirring, monitoring and flow control apparatus as needed. Inthis respect, the presence of impurities within the raw materials mayprovide a seed for precipitation or crystallisation at later stages,which could result in the production of an unstable product. As themethod of the invention aims at avoiding precipitation of coppersilicate in particular, filtration may also be utilised as necessary.

In the method of the invention, it is believed that the sodium of thesodium silicate is neutralised by the excess acetic acid and creates thepreviously described buffer system. It is also believed that the copperreacts with the excess silicate to form copper silicate which ismaintained in solution by the buffer. Other chemical species present maybe sodium sulphate and sulphuric acid. Furthermore, while the activeingredient in the subsequently obtained residue is acidic coppersilicate, other compounds may coexist, such as copper sulphate, copperacetate, sodium silicate, sodium acetate, acetic acid, silicic acid,sodium silicate and sulphuric acid, or any such combinations.

Finally, and as indicated above, the product of the invention may beconverted for use in a solid form as desired for a particularapplication. For example, the product may be sprayed onto an absorbentgranule such as attapulgite or montmorillonite clays, although a varietyof other carriers such as expanded perlite, exfoliated vermiculite andcalcium carbonate granules could be used. In this respect, it will beappreciated that the type of carrier used will be substantiallydependent on the environment in which the product will be used and alsothe particular type of use required.

After spraying the product onto a chosen carrier, the carrier grannulesmay be dried, leaving the copper silicate residue upon and within thegranules. The granule size is preferably in the range of 0.1 to 5 mm,although other size ranges may be appropriate and may be used if needed.In this respect, it is also envisaged that the product may be used withpowders, whether they be adsorbent or absorbent, such as talc powder(adsorbent) or kaolin clay and diatomite (absorbent). Of course, whenusing the adsorbent, the residue after drying remains only on theoutside of the particles.

Those skilled in the art will also appreciate that there may be othervariations and modifications of the method and product described hereinwhich are also within the scope of the present invention.

What is claimed is:
 1. A method of producing a copper silicate product,comprising reacting a copper salt with an alkali silicate in an acidicsolvent to produce an aqueous solution of acidified copper silicatecapable of being used as a fungicide or pesticide.
 2. A method accordingto claim 1 wherein the acidic solvent buffers the mixture of copper saltand alkali silicate such that the acidified copper silicate has a pH inthe range of 2 to
 6. 3. The method according to claim 2 wherein the pHis in the range of 3 to
 5. 4. The method according to any one of claims1 to 3 wherein the acidic solvent comprises acetic acid and sodiumacetate.
 5. The method according to claim 4 wherein the acetic acid andsodium acetate are in a ratio of between 1:5 and 5:1 and in aconcentration of 0.01 to 10% w/w.
 6. The method according to claim 1wherein the copper salt is copper sulphate.
 7. The method according toclaim 6 wherein the copper sulphate is copper sulphate pentahydrate andis present in an amount in the range of 0.1 to 25% w/w.
 8. The methodaccording to claim 1 wherein the alkali silicate is sodium silicate. 9.The method according to claim 8 wherein the sodium silicate has a ratioof SiO₂ to Na₂ O of from 3.75:1 to 1:2, and is present in an amount inthe range of 0.05 to 20% w/w.
 10. The method according to claim 1wherein the copper salt is copper sulphate pentahydrate in an amount inthe range of 0.5 to 10% w/w, the alkali silicate is sodium silicatehaving a ratio of SiO₂ to Na₂ O in the range of 2.5:1.5 to 3.5:2.5, a pHrange of 10 to 14 and in an amount in the range of 0.2 to 5.0% w/w, andthe acidic solvent is an acetic acid/sodium acetate buffer system havingacetic acid in an amount in the range of 0.05 to 2.0% w/w.
 11. Themethod according to claim 1 wherein the copper salt, the alkali silicateand the acidic solvent are each separately diluted with water and atleast the copper salt is allowed to stand for between 8 and 24 hours,the acidic solvent is then added to the diluted copper salt withstirring, and the alkali silicate solution added thereafter withstirring, following which the mixture is diluted with water.
 12. Amethod of producing a copper silicate product for use as a fungicide orpesticide, the method comprising preparing in separate batches (1)diluted copper sulphate, (2) diluted sodium silicate, and (3) an aceticacid buffer, adding the acetic acid buffer to the diluted coppersulphate, then adding the diluted sodium silicate to this mixture, toproduce a stable, silicate rich, aqueous solution of acidified coppersilicate having a pH in the range of 3 to
 5. 13. A copper silicateproduct produced by the method of claim
 1. 14. A copper silicate productproduced by the method of claim
 12. 15. A copper silicate product foruse as a pesticide or herbicide, said product being a stable, silicaterich, aqueous solution of acidified copper silicate having a pH in therange of 3 to 5.